Multiplex transmission



2Q; 393@ R, H, RANGER MULTIPLEX TRANSMISSION Filed Jan. 5, 1933 2 Sheets-Sheet l Sash INVENTOR ATTORNEY ...h Mm

@am 2g? E936. R M RANGER MULTIPLEX TRANSMISSION Filed Jan. 5, 1953 2 ySheets-Sheet 2 MKM.

kvm,

NAM

www.

Vix

www

, .NNN

www.

INVENTOR memo HowLANn RANGER BY if@ AWORNEY ill atentec Jan. 28, 1936 Unirse STATES( PATENT orales 2,028,805 ETULTIPLEX TRANSMISSION Richard Howland Ranger, Newark, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application January 5, 1933, Serial No. 650,215 7 Claims. (Cl. Z50-9) The present invention relates to a multiplex transmitting instrumentality without causing the so-called cross talk or interference between 5 signals may be transmitted.

According to a preferred form for keying both or to provide two separate receivers, one being for the sound signals and the other for telegraphic signals.

primary objects system for simul that of providing a transmission taneously transmitting a plurality of signals without causing interference between the various transmitted signals.

nals of different characteristics without any possibility of so-called cross talk between channels.

one which is supposed to distinguish the particular signal. In this manner the voice and/or telegraph signals and/or light signals cannot interfere one with the other.

Fig. 1 illustr-ates one suitable form of transmitter circuit arrangement; and

4sumed to be a Vrihe generated oscillations from the plate potential source 52.

a 2,028,805 lation system 5, telegraphlc or picture signal 51, @9 are then impressed upon the input elecmodulation systems 5 and 9, a combining unit 1 for the carrier frequency oscillator 8, having its frequency doubled in a plurality of carrier frequency doubling stages 9 and lli located interthe carrier frequency generator 8 and the combining unit i, whose output is amplified in a plurality of linear amplifying stages l2 andA is and then transmitted by way of a transmitting device lll.

To refer now more specifically to the particular circuit arrangement which has herein been shown and described as illustrating one form of system to practice the invention, it is seen that one tone or carrier frequency of intermediate value, which for convenience of illustration may Vherein be as- 3 kc. tone, is generated in the oscillation generator tube 2| havingvconnected with itsr output electrode a Yresonant circuit 23 comprising indnctance 25 and capacity '21 The output electrode of the tube 2| is energized by way of a potential source 28 shunted by a variable capacity element 29Var1d across the input circuit is apiezo electric crystal control V3| shunted by the resistor element 33. The generated frequencies from the oscillator 2| appearing in the tank or resonant circuit 23 are then transferred to the secondary 31 of the transformer comprising the inductance 25 ofthe plate circuit and the Winding 31 to be supplied to the input electrode of an amplifier 35, from the output of Ywhich they are transferred to be impressed upon the input electrodesof a pair of push-pull connected amplifier tubes E'iand 59.

Simultaneously with the generation of a low frequency tone carrier by the oscillation generator 2| a higher frequency tone or quency carrier, herein assumed to be 100 kc., is generated in the oscillator 39 having connected with its plate electrode a tant: circuit 4| comprising an inductance element 43 forming the primary of a transformer and a capacity element 45. Similarly to the oscillator 2l the frequency generated and appearing in the tank circuit Si is 'controlled by way of a crystal control 5|, which crystal 5| shunted by a resistor element 53. tank circuit appear in the inductance primary of a transformer and arerthen transferred to a plurality of secondary coils or windings 55 and |95. From thev winding 55 the generated signals of xed frequency are -supplied to the push-pull amplifier stage comprising the tubes 51 and 59 having the grid electrodes thereof suitably biased by way of a biasing source t! and having the plate electrodes energized from a common The generated frequency of the oscillator 39 is supplied to the push-pull stage comprising tubes 51 and 59 by way of a carrier suppression modu lator systemiso that in the output circuit of the tubes 51 and 59, formed as the primary winding t9 of the transformer 53, 65, there appears frequencies of 9'1 kc. for example and 103 kc., for example, which correspond to the upper and lower side bands formed by beating a 100 kc. generated frequency from the oscillator 39 with the 3 kc. generated frequency from the oscillator 2|.

If now it is desired to produce a plurality of telegraphic signals or, for example, picture controlled signals, these signals may be impressed at the signal inputs generally designated A and BVi and supplied across a series of terminals |31, 59 and 1|, 13, respectively. The signals sup= plied inthe channel A across the terminals intermediate fref prising the inductance 95 of Yinput circuit of an amplifier trode of a vacuum tube amplifier across a resistor element 11. The input electrode of the tube 15 is normally biased positively by way of a biasing source 13 so that in the absence of signals across the ternnnals 61, V69 plate cul"- rent which is supplied by way of a Vplatesupply source 19 to the tu -e 15 will iiow and thus produce a substantial voltage drop across theresistor 8| which produces a change in potential at the point of connection of the conductor 83 with the potential source i9 and. the resistor 8| to carry this point more negative and thus change the effective biasing voltage supplied by the biasing battery 85 through the conductor 81 to the push-pull connected amplifier tubes 89 and 99 so as toy prevent the tubes 89 and 9|) from passing current supplied thereto from the oscillator tnbe 9| comprising the usual electrode elements 92, 93 and 94.

The oscillator 9| is not inherently stable but is of the general type known as the Hartley oscillator and comprises the split plate coil 95 to the midpoint of which the cathode electrode of the vacuum tube 9| is connected and which split plate coil 95 is shunted by a variable Vcapacity 91. Energy is supplied to Ythe plate circuit of the oscillator Y9| from a plate potential source 98 and the frequency generated in the osciilator, which may herein be assumed to be substantially of the order of 103 kc., which is the resonant frequency of the tuned circuit comprising the inductance 95 and the variable capacity t1 is then adapted to be locked ulating the 100 kc. tone, assumed to be generated by the oscillator t9, by the 3 kc. tone, assumed to be generated by the oscillator 2|, which beat frequency appears in the transformer output 63 of the pmsh-pull stage comprising vacuum tubes 51 and 5t.V I n The frequencies corresponding tothe upper Vand lower side bands, assumed to be 97 to 103 kc.,

are transferred from the primary 53 to the secondary winding 65 from which they are by way of the Vconductor 99 through a winding 00 and thence through the conductor |0| through a winding |02 and conductor |t3 back to the transformer secondary 65. The frequenoies iiowing through the winding |02 whichV are adapted to be impressed by way of the coupling existing between the winding 02 and the inductance 95 of the oscillator circuit serve to lock l the oscillator 9| at its normally generated frequency so that the energy transferred to the secondary winding |04 of the transformer comthe oscillator 9| |04 is then impressed upon the |05 whose output is connected to the push-pull stage comprising tubes 89 and 99 through the. transformer formed from the windings |06 and |01.V

If now signals are impressed upon the signal input stage A and across the terminals 61 and 59 so that the signal applied at terminal 61 is negative and the signal applied at terminal 69 is positive it can be seen that the grid electrode of the tribe 15 will be carried negative to a point sufcient to cut-od the plate ycurrent flowing in the output circuit of the tube.:

and the winding the grids of the push-pull tubes 89 and 90, cnrrent flows in the output circuit of theV push-pull stage. Y i

Assuming' now that the oscillator 9| is genby one of the side .band frequencies generated as a beat frequency produced by modconveyed y Then, by virtue Y of the increase in the effective voltage acting upon age for the ampliers 89 and 90 is supplied from frequency interthrough a transformer secondary I|3 to vacuum tube amplifier |21 Whose plate circuit includes the plate potential source |29 and the transformer primary ISI.

Similarly, the oscillator system comprising the oscillator tube |35 having plate, grid and filament |39 and |4| of which the plate plate voltage source on the oscillator |35, appearing in the Winding |09 connected with the secondary Winding S5 of the transformer E3, 65 so that the frequency of the oscillator |35 is now stabilized at 97 kc. by the constant frequency generated in the oscillators I and 2. This 97 kc. frequency is then impressed tubes ITI and |79. channel B which taneously with the the second are to be transmitted simulsignals from the iirst channel battery I 99 of a frequency of 97 kc.

secondary Winding |33 of the transformer having the split primary |94, ISI and 229.

Simultaneous with this application of frequenquency herein-above assumed to be 100 ks., as was above pointed out. The generated frequencies at 1GO kc. appearing in the tank or resonant circuit f3! of the oscillator tube 39 are impressed not only upon the transformer secondary but also upon the transformer secondary |93 from which they are transferred to the amplher tube |95, which is energized by a battery |97, so as to appear in amplified form in the transformer primary |99 connected in the output circuit of the tube |95. transformer Winding 20| the 100 kc. energy is supplied to the input circuit of an amplifier tube 203.

The sound signals which are assumed to beimpressed upon the microphone 205 are transferred therefrom to the amplifier 201, which is suitably biased by Way of a biasing source 209.

of the plate current flowing in the output circuit of the tube 207, which circuit includes the inductance put of the tube The modulator tube 203 has connected in its output circuit a variable capacity element 2|`| and the transformer primary 2|9 which form together a resonant circuit of plate current modulation system.

The modulated 1D0 kc. voltage energy from tube 293 is then transferred by Way of the inductance 2 t9, forming the primary of a transformer, to the secondary element the Winding |33. The output circuit of tube 225 is then completed by way of a conductor 23| connected to the plate current source 235.

l'f it is assumed that the sound modulation ls To produce a carrier frequency for transmission there is provided an oscillator unit 8 Awhich winding 2li of a and their output cil is vof substantially standard and well known form.

The oscillator or generator unit 8 includes an oscillation generation tube 231 having plate, grid and filament electrodes 233, 2M and 203, respectively, -of which the plate electrode is connected to ground at 230 by way of a resonant circuit including the parallel combination of inductance and capacity 235, 231 which connects with the cathode or nlament electrode of the tube by way of a plate current source 23B. The tube grid electrode 2li! is connected to ground through the series combination of a resistance 250 and inductancev and capacity elements 253 and 259 all of which are connected in parallel with the piezo -1 electric crystal frequency control element 263,

so that the frequency generated by the oscillator tube 231 is stabilized by way of the crystal control element 233. To supply a suitable biasing potential to the tube 231 a biasing source may Y be connected with the grid electrode by way of the inductance 253 and resistance 250 at the terminal 255.

The generated frequencies of the oscillator tube 231 are then supplied to an amplifier tube 233 by way of a capacity coupling 261. The output circuit of the tube 209 comprises the primary transformer and the plate current source 213 so that the amplified oscillation frequencies are supplied to the transformer secondary 215 from the plate inductance 21! and thereby caused to energize the input circuit of the frequency doubling stage comprising the tubes 211 and 21e. The tube 211 and 210 are connected with their inputs in push-pull and supplied with current from the source 23i by way of the transformer primary 283. The currents flowing in the output circuit of tubes 211 and 213 cause proportionate voltages to be supplied to the secondary winding 205 of the output transformer. The secondary of this transformer connects by waryV of conductors .231, 283 and the center-tap conductor to the input circuit of a second frequency doubling stage comprising the tubes 293 and 295 having their input circuits connected in push-pull circuits in common so that the output energy at double the input frequency appears in the winding 291. This double frequency energy is then transferred by way of the secondary winding 230 to the tubes 303 and 305 which are suitably biased from they energy source and signal energized also by way of the transformer secondary H33 so as to be modulated or controlled in accordance with the signals appearing in the signal input channels A, B, C,

It is'preferable to supply across each frequency doubler stage a tuning capacity, as shown,y in order to tune the output system to the doubled frequency, but this is not absolutely essential and,

where desired, the tuning capacities may be omitted.

The push-pull amplifier stage comprising the tubes 303 and 335 is, as shown above, supplied with energy at a frequency which is four times the generated .carrier frequency. This push-pull stage is arranged as a carrier suppression stage. These tubes 3533 and 335 are supplied with energy from a plate current source 303. The output circuit is tuned by wayof the resonant combination -of inductance 301 and capacity 308 to any desired frequency, for example, assume that oscillator 8 is set at 1500 kc. and with the twice doubling becomes 6000 kc. in transformer 231, 293. Then by modulation of the intermediate frequencies introduced into stage? in Vthe secondary |33, two side bands are produced. Then the output circuit 301 and 308 is tuned to a frequency of 6100 kc. so that due to the modulation of the carrier frequency by the two telegraphic or picture signal inputs and/or the sound signal input' there appearsin the resonant circuit comprising 301 and capacity' 300 signals of a frequency of 6097, 6100 as modulated by the 2500 cycle sound modulation and 6103 kc. provided, of course, that these are all passed by the 6100 kc. tuning and that the lower side band frequencies are suppressed due to the above suggested tuning selected. These signals at the above frequencies, which are assumed purely for the purpose of illustration and not in any sense with a View to limiting the scope of the invention since wide variations in selected frequencies may be made, are then. again amplified in the linear amplifier stage. This amplifier is what has become known in the art as a class A amplifier Vand is ideally suited to the. purpose of reducing any possible cross tal between the several channels of the system. The amplifier stage comprises. the push-pull amplifiers 3|5 and 3 l1 which have their input circuit suitably biased by the biasing source 313 and the input circuits suitably tuned to the selected frequency by way of a capacity element 3|2. Operating current is supplied from a source 3i3. The tubes 315 and 3l1 are supplied with controlling signals through the secondary Winding 3H yof the input transformer which has its end terminals connected to the tube input electrodes. The modulated signals appearing in the output circuit of the push-pull stage 3 l 5, 3|1, which output circuit comprises the resonant combination of inductance 32! and capacity 322, here again tuned to 6100 kc., still ful'- ther yselects the above-named frequencies with additional discrimination with respect to the lower side band frequencies. These frequencies, as amplified, are then supplied to the transformer secondary 323 to energize the push-pull tubes 321 and 329 by way of a tuned input circuit comprising the transformer secondary 323 and capacity 324, also tuned to 6100 kc. as inthe previous stage. The amplifiers 321 and 329 are suitably biased by way of a biasing source 325 and receive their plate current from a source 33|.

The output circuit of the push-pull stage 321, 329 includes the resonant circuit comprising the transformer primary 333 and the capacity 334 which is also tuned to Y6100 kc. to discriminate against the lower side band frequencies pro-duced from modulating the carrier frequency supplied to the push-pull stage 303,. S05-by the sound and picture or telegraphic signals so that whatever signals now Lappear in 333 may be supplied to the secondary winding 335 of the transformergrounded at 331 so as to be radiated by the antenna I4 or by way of a suitable wire line connection to various receivingV points. Y

The energy now transmitted from the antenna or any other suitable form of transmitting device I4 may then be received on a plurality of independent receiving instrumentalities comprising the antennae 350, 352, 355 from which the received signals are directed to the receivers 356, 353 and 330, respectively, which may be, where desired, the usual type of superheterodyne receivers tuned to suitable frequencies by means of a local oscillator. The output of the sound signal receiver. 353 at the transformer primaryV l00 kc. is then suitably amplified in an amplifier 302 and transferred through a low-pass lter 354 which is arranged to cut-on at2500 cycles, which Was above assumed to be the limit of modulation arrangement by sound signals, and then passed to a sound producer 366.

The signals for telegraphic or `picture signal transmission channel A are received in the receiver system 358 mission channel B are received system 360. generating for generated by the said local oscillator, signals o1' a frequency of 8 kc. which are suitably amplified in the amplier 372. The signals from the amplier 370 which are assumed to be at 2 kc. are then passed through the low-pass iilter 374, which is also arranged to cut-off at 2500 cycles, and supplied to a recorder or the like 316.

producing arrangement 380. that the sound signals and the picture or telesimultaneously 4three separate and distinct messages.

In accordance with the arrangement herein shown it is, of course, obvious that many changes and departures may be made from theparticular disclosed herein Without departing distinct input circuits like those shown as A, B and C. Such a system would also require one master oscillator for producing the carrier frequency, a master oscillator for producing inand two audio frequency In like manner a greater number of channels could be used.

A receiver device capable of modulated up and the other is modulated down and the output from both is maintained l.l In a multiplex transmission system the method which comprises generating a plurality of intermediate frequency, producing from the generated carrier frequencies side band side band frequencies modulating each produced Y side band stabilized frequency and at least one generated carrier frequency independently by ,signals representative of the intelligence to be cornmunicated, generating fa transmission carrier frgequency, modulating the transmission carrier Vfoy each Q-of the modulated intermediate carrier frequencies, suppressing one side bandfrequengcy produced by the modulation of the carrierf'requency by each modulated intermediate carrier, amplifying the modulated transmission carrier frequency, tuning the amplifying system sharply to the selected side band frequency produced by modulation, and transmitting the modulated carrier frequency representative of -the intelligence signals supplied to all channels of the multiplex system. f. Y

2. The method of` mul lexing signals for transmission Which comprises generating a plurality of l intermediate frequencies of consta-nt Value, producing from the intermediate frequencies side band frequencies by modulating one by the other, generating frequencies corresponding substantially to the produced side band frequencies, locking the substantially constant generated frequencies independently by each of the produced side band frequencies, modulating one intermediate frequency generated and the controlled side band frequencies independently of each other to produce simultaneously a plurality of.: relatedsignals representative of thel intelligence to be communicated upon each channel of the multiplex system, generating a transmission carrier frequency, and modulating the transmission carrier by each of the modulated intermediate frequencies produced. i i

.3. The methodV claimed in claim 2 comprising,

v in addition, suppressing one of Ythe side bands rproduced by each modulated intermediate frequency, modulating the transmission carrier frequency. 1;

Y 4. The method claimed in claim 2 comprising, in addition, linearly amplifying-,the modulated transmission carrier frequency prior tojtransmission so as to avoid interference between the signals in each independent signal channel of the multiplex system. ia

5. 1n a multiplex signal transmitting system, a plurality 'ofsignal energized circuits each responsive to impressed intelligence signals, a pluralityl of stable? generators ofY intermediate frequency; a plurality of unstable generators of intermediate frequency,

stabile generators to s nels.

erators to maintain fixed frequency spacing-and relationshipbetween each generated frequency, means for modulating each controlled` interme- 5 Y diate frequency source by the signals of a coordinated signal energized circuit, and means to control the transmission of energy simultaneously by the modulated intermediate'frequency sig- 6. A signalling system comprising a source of carrier frequency energy, la constant frequency generator of intermediate frequencies, a constant means controlled bylthe tabilize the unstable Vgenfrequency generator of lovgl frequencies, means to 15 produce bythe combined'output of both generators intermediate frequency side band frequen-` cies, means to generate intermediate frequencies corresponding in ffalue to the side band frequencies, means to stabilize the last named frequency 2o sources by the produce quency an independen input circuit, and rn modulated intermediate frequencies.

d side band frequencies, a i pluralitylof independent signal controlled input circuits, means to modulate each intermediateY frequency corresponding to the side band fre-V d the intermediate frequency carrier 'V25 tly of each other by thesignals appearing in a single coordinated signal controlled i eans to modulate the carrier frequency for transmission by eaclq of the of sources of intermediate frequency, a plurality of signal controlled circuits independently connected with each intermediate frequency sourceto modulate each independently'of the Yother in 35 accordance With the signals applied thereto, a v low frequency source, means to produce from one and the low frequency source side band frequencies torrlock the remaining intermediate frequency sources at the pro- 40 duced side band frequencies, asource of carrier frequency energy, means to modulate theA produced carrier frequency band frequency and one frequency, means to suppre quencies produced on one si y mdulation, an

high frequency sourceV quency lo each indepe by each modulated side modulated intermediate ss the side 'band fre- 45 de Vof the carrier fred means to amplify linearly all the modulated frequencies to prevent interference in reception between the signals of ndent lsignal energized input. i 

